GBAS CAT II/III Operational Validation Input for Business Aircraft – Flight Tests and Simulations

Jolana Dvorska, Ladislav Podivin, Lenka Zaviralova, Martin Musil, Michal Kren

Abstract: ABSTRACT In order to support GBAS CAT II/III (GAST D) validation, an extensive flight test campaign was carried out in Sep/Oct 2013 with Honeywell flight test aircraft Dassault Falcon 900EX – Phase 1 and recently, Phase 2, was carried out in Jun/Jul 2014. This paper focuses on Phase 2. The aircraft was equipped with a prototype GAST D avionics receiver that was coupled with the autopilot of the CAT II capable aircraft. Testing in Phase 2 was performed on five different airports, with five different ground stations from three manufacturers, in the US and in Europe. The ground and airborne equipment was at its final prototype functionality. Since flight tests typically only show nominal performance of the overall system and cannot comprise corner cases, Monte-Carlo approach and landing simulations covering nominal, limit and malfunction cases must be performed to show the overall system compliance with the Autoland requirements. In order to collect all the data needed with respect to the objectives, the experimental aircraft was equipped with an airborne receiver prototype with GBAS GAST D final capability, a Novatel survey grade dual-frequency receiver (SPAN) for truth measurements, a Telerad RE9009 VHF receiver and Multi-constellation multi-frequency (MC/MF) receiver prototype. The three GPS/GNSS receivers were all connected to the same GNSS dual frequency antenna. VHF Data Broadcast (VDB) for the three relevant receivers (in this case the GBAS prototype, Telerad and MC/MF) are connected to the same VHF NAV/LOC antenna situated at the top of the vertical fin of the experimental aircraft. The ARINC 429 outputs of the GBAS prototype are coupled with the autopilot. The Phase 2 flight plan covered a total of 95 approaches to collect sufficient amount of data. Phase 2 focused on 9 scenarios, including data collection for multipath performance testing, interoperability validation, airborne regressions to CAT I approach (GAST C) and non-regression GAST C approaches. Detailed analysis of results was performed, including navigation system error evaluation, total system error as well as performance of the required monitors and their impact on availability of the solution. Navigation sensor error and total system error were analyzed and are showing good performance. Analysis with respect to the airborne multipath was performed also for Phase 2 and results shown are confirming expectations - multipath performance on a larger business aircraft not quite conforming with the RTCA multipath model, but in line with the multipath plus noise requirements leading to reasonable sigma error estimates. Monitor performance was analyzed and was conforming to expectations during nominal conditions. Downgrades to lower approach service type was observed during the testing caused by Fault Detection during approach and taxi phases; further analysis led to the conclusion that improved specification of the monitor is required. This update is currently under development. Dual solution ionospheric gradient monitor caused downgrades only while stationary, due to increased levels of ground multipath as well as reflections off nearby buildings, which does not affect the GAST D operation. Observed satellite exclusions were caused by the Code-Carrier Divergence monitor, which is very much in line with expectations. The exclusion of satellites exceeding the filter threshold never caused downgrade or loss of availability. Corrections and finalization of both ground and airborne parts in Phase 2 resulted in better navigation performance than in Phase 1. The overall GBAS Navigation system performance was improved compared to Sep/Oct 2013. The improved NSE can be explained by improvements in both airborne and ground systems, as well as by more data collected. Overall, the flight tests were very successful and support the concept validation. With respect to the simulations, a Honeywell legacy simulation tool consisting of models of generic business aircraft with receiver model upgraded to GAST D capability, ground station model including reference receivers, constellation model and error models such as ionospheric, tropospheric, multipath and noise was used for the Monte-Carlo simulations based on requirements from regulatory bodies. It was confirmed that the navigation sensor error observed during the flight tests is within the used model which is consistent with AWOHARC GBAS noise model that may be used to show compliance with approach and landing requirements. Overall 18 scenarios (with close to 300,000 simulation runs), including different generic A/C and autopilot models (FTE), almanacs, NSE model and airport set, were simulated during feasibility analysis and the results were statistically analyzed to show if the compliance with landing requirements defined by CS-AWO is met. Nominal and limit cases performed within expectations and complied with requirements. Since the autoland simulations use generic autopilot assumptions, the result shows the theoretical capability of business aircraft with the assumed touchdown distribution meeting the landing requirements when using GBAS GAST D. The feasibility generic simulations pointed to short steep ramp faults close to ca 200ft within malfunction case which in a few cases resulted in shorter approaches (but still within the runway). Although a more robust A/C control system behavior with an appropriate filtering or control system limitations than in the presented generic model is expected, it is highly recommended that this possible threat is well reviewed and confirmed by airframe manufacturers that it is covered.
Published in: Proceedings of the ION 2015 Pacific PNT Meeting
April 20 - 23, 2015
Marriott Waikiki Beach Resort & Spa
Honolulu, Hawaii
Pages: 779 - 798
Cite this article: Dvorska, Jolana, Podivin, Ladislav, Zaviralova, Lenka, Musil, Martin, Kren, Michal, "GBAS CAT II/III Operational Validation Input for Business Aircraft – Flight Tests and Simulations," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 779-798.
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